Improving Voice Outcomes After Thyroid Surgery - Review of Safety Parameters for Using Energy-Based Devices Near the Recurrent Laryngeal Nerve.

Technological advances in thyroid surgery have rapidly increased in recent decades. Specifically, recently developed energy-based devices (EBDs) enable simultaneous dissection and sealing tissue. EBDs have many advantages in thyroid surgery, such as reduced blood loss, lower rate of post-operative hypocalcemia, and shorter operation time. However, the rate of recurrent laryngeal nerve (RLN) injury during EBD use has shown statistically inconsistent. EBDs generate high temperature that can cause iatrogenic thermal injury to the RLN by direct or indirect thermal spread. This article reviews relevant medical literatures of conventional electrocauteries and different mechanisms of current EBDs, and compares two safety parameters: safe distance and cooling time. In general, conventional electrocautery generates higher temperature and wider thermal spread range, but when applying EBDs near the RLN adequate activation distance and cooling time are still required to avoid inadvertent thermal injury. To improve voice outcomes in the quality-of-life era, surgeons should observe safety parameters and follow the standard procedures when using EBDs near the RLN in thyroid surgery.

Intra-Operative Neural Monitoring of Thyroid Surgery in a Porcine Model.

Intraoperative injury to the recurrent laryngeal nerve (RLN) can cause vocal cord paralysis, which interferes with speech and can potentially interfere with breathing. In recent years, intraoperative neural monitoring (IONM) has been widely adapted as an adjunct technique to localize the RLN, detect RLN injury, and predict vocal cord function during the operations. Many studies have also used animal models to investigate new applications of IONM technology and to develop reliable strategies for preventing intraoperative RLN injury. The aim of this article is to introduce a standard protocol for using a porcine model in IONM research. The article demonstrates the procedures for inducing general anesthesia, performing tracheal intubation, and experimental design to investigate the electrophysiological characteristics of RLN injuries. Applications of this protocol can improve overall efficacy in implementing the 3R principle (replacement, reduction and refinement) in porcine IONM studies.

Feasibility of Intraoperative Neuromonitoring During Thyroid Surgery Using Transcartilage Surface Recording Electrodes.

BACKGROUND: Intraoperative neural monitoring (IONM) has gained widespread acceptance as an adjunct to the gold standard of visual identification of the recurrent laryngeal nerve (RLN) during thyroid surgery. Currently, laryngeal electromyography (EMG) recording during IONM is almost always performed using endotracheal tube (ETT) surface electrodes placed adjacent to vocal folds originating from the inner surface of the thyroid cartilage (TC). Therefore, it was hypothesized that surface recording electrodes placed on the outer surface of the TC should enable access to the EMG response of the vocal folds during IONM. The aim of this experimental study was to evaluate the feasibility of the transcartilage approach for laryngeal EMG recording during IONM. METHODS: A porcine model (12 pigs and 24 RLN sides) with well established applicability in IONM research was used for the experiments. Both ETT electrodes adjacent to vocal folds and adhesive pre-gelled electrodes on the TC were used for EMG recording during IONM. Electrically evoked EMG signals detected by both electrode types were recorded and analyzed. EMG changes during tracheal displacement and RLN traction injury were compared. RESULTS: Both the ETT and TC recording electrodes recorded typical laryngeal EMG waveforms evoked by a 1 mA stimulus current applied on both sides of the RLNs and vagus nerves (VNs). Under RLN stimulation, the mean EMG amplitudes recorded with the ETT and TC electrodes were 973 ± 79 µV and 695 ± 150 µV, respectively. Under VN stimulation, the mean amplitudes were 841 ± 163 µV and 607 ± 162 µV, respectively. When upward displacement of the trachea was experimentally induced, the TC electrodes showed less variation in recorded EMG signals compared to ETT electrodes. When RLN traction stress was experimentally induced, both the ETT and TC electrodes accurately recorded the typical EMG pattern of progressively degrading amplitude and gradual recovery after release of traction. CONCLUSIONS: This study confirms the feasibility of using transcartilage surface electrodes for recording laryngeal EMG signals evoked during IONM in an animal model. However, before practical application of this approach in clinical thyroid surgery, further studies are needed to improve electrode designs by optimizing their shapes and sizes, and increasing their adhesive stability and sensitivity.

Safety of high-current stimulation for intermittent intraoperative neural monitoring in thyroid surgery: A porcine model.

OBJECTIVES: During monitored thyroidectomy, displacement of the recurrent laryngeal nerve (RLN) or vagus nerve (VN) in some complicated cases can increase the risk of injury. Although increasing the stimulus current can facilitate nerve mapping and localization, the safety of a high-current stimulus remains unknown. Therefore, this study evaluated the safety of a high-current stimulus in a porcine model. METHODS: Short-duration (1 minute), high-current (3, 5, 10, 15, 20, 25, and 30 mA at 4Hz) stimulus pulses were repeatedly applied to the RLN or VN in six anesthetized piglets. The safety of the high-current stimulus pulses was assessed in terms of hemodynamic stability during VN stimulation and in terms of nerve function integrity after VN and RLN stimulation. RESULTS: During VN stimulation with a high-current stimulus pulse, sinus rhythms in all six piglets showed stable heart rates, and mean arterial pressure was unaffected. High-current stimulation of the VN and the RLN did not affect electromyography amplitude or latency. CONCLUSION: This porcine study showed that applying a short-duration, high-current stimulus pulse to the VN or RLN during monitored thyroidectomy has no harmful effects. In clinical practice, a short duration of high-current stimulus can be applied to facilitate neural mapping, especially in patients with disoriented nerve positions. LEVEL OF EVIDENCE: NA. Laryngoscope, 128:2206-2212, 2018.

Trachway video intubating stylet allows for optimization of electromyographic endotracheal tube placement for monitored thyroidectomy.

BACKGROUND: Endotracheal tube-based surface electrodes are now commonly applied to measure evoked electromyographic (EMG) response of the vocal cord during monitored thyroidectomy. The aim of the study was to determine the incidence of difficult intubation and to assess the effectiveness of using video-assisted intubating stylet (Trachway) for EMG tube placement in patients undergoing monitored thyroidectomy. METHODS: Medical records were collected from consecutive patients undergoing thyroid surgery before and after implementation of the protocol. A total of 748 patients intubated with EMG tube for monitored thyroidectomy by the same team were enrolled in this study. Patient allocation was based on intubation technique either conventional direct laryngoscopy (n=336) or Trachway (n=412). The intubation difficulty was assessed and analyzed. RESULTS: The overall incidence of difficult intubation was 4.4%. Incidence of difficult intubation was significantly lower in patients with the Trachway procedure (2.7%) than direct laryngoscopy (6.5%, P=0.01). The incidence of "unable to intubate" (>3 attempts, or change airway device or anesthesiologist) also significantly reduced from 2.3% to 0.5% after introduction of the Trachway intubating stylet (P=0.02). CONCLUSIONS: We conclude that the incidence of difficult intubation was significantly lower with Trachway than direct laryngoscopy. The Trachway video-intubating stylet is useful and helpful to reduce EMG tube intubation difficulty for monitored thyroidectomy.

Preoperative, intraoperative and postoperative anesthetic prospective for thyroid surgery: what's new.

The aim of this review is to analyze what's new on anesthetic prospective to perioperative management for thyroid surgery. For recent decades intraoperative neuromonitoring (IONM) during thyroid and parathyroid surgery has obtained more and more popularity. New modality of anesthetic technique was also developed to incorporate into surgical teamwork. For example, the precise position of EMG tube and optimal use of neuromuscular blocking agents (NMBAs) play key roles in successful IONM system. Special focus is paid to following issues: (I) preoperative airway evaluation and pre-op preparation; (II) anesthetic managements including advanced intubation tools, NMBAs and sugammadex; and (III) post-op adverse events such as pain and postoperative nausea vomiting.

The feasibility of sugammadex for general anesthesia and facial nerve monitoring in patients undergoing parotid surgery.

The use of neuromuscular blocking agent (NMBA) during anesthesia may interfere with facial nerve monitoring (FNM) during parotid surgery. Sugammadex has been reported to be an effective and safe reversal of rocuronium-induced neuromuscular block (NMB) during surgery. This study investigated the feasibility and clinical effectiveness of sugammadex for NMB reversal during FNM in Parotid surgery. Fifty patients undergoing parotid surgery were randomized allocated into conventional anesthesia group (Group C, n = 25) and sugammadex group (Group S, n = 25). Group C did not receive any NMBA. Group S received rocuronium 0.6 mg/kg at anesthesia induction and sugammadex 2 mg/kg at skin incision. The intubating condition and influence on FNM evoked EMG results were compared between groups. The intubation condition showed significantly better in group S patients than C group patients (excellent in 96% v.s. 24%). In group S, rapid reverse of NMB was found and the twitch (%) recovered from 0 to >90% within 10 min. Positive and high EMG signals were obtained in all patients at the time point of initial facial nerve stimulation in both groups. There was no significant difference as comparing the EMG amplitudes detected at the time point of initial and final facial nerve stimulation in both groups. Implementation of sugammadex in anesthesia protocol is feasible and reliable for successful FNM during parotid surgery.

Reversal of rocuronium-induced neuromuscular blockade by sugammadex allows for optimization of neural monitoring of the recurrent laryngeal nerve.

OBJECTIVES/HYPOTHESIS: The use of neuromuscular blocking agent may effect intraoperative neuromonitoring (IONM) during thyroid surgery. An enhanced neuromuscular-blockade (NMB) recovery protocol was investigated in a porcine model and subsequently clinically applied during human thyroid neural monitoring surgery. STUDY DESIGN: Prospective animal and retrospective clinical study. METHODS: In the animal experiment, 12 piglets were injected with rocuronium 0.6 mg/kg and randomly allocated to receive normal saline, sugammadex 2 mg/kg, or sugammadex 4 mg/kg to compare the recovery of laryngeal electromyography (EMG). In a subsequent clinical application study, 50 patients who underwent thyroidectomy with IONM followed an enhanced NMB recovery protocol-rocuronium 0.6 mg/kg at anesthesia induction and sugammadex 2 mg/kg at the operation start. The train-of-four (TOF) ratio was used for continuous quantitative monitoring of neuromuscular transmission. RESULTS: In our porcine model, it took 49 ± 15, 13.2 ± 5.6, and 4.2 ± 1.5 minutes for the 80% recovery of laryngeal EMG after injection of saline, sugammadex 2 mg/kg, and sugammadex 4 mg/kg, respectively. In subsequent clinical human application, the TOF ratio recovered from 0 to >0.9 within 5 minutes after administration of sugammadex 2 mg/kg at the operation start. All patients had positive and high EMG amplitude at the early stage of the operation, and intubation was without difficulty in 96% of patients. CONCLUSIONS: Both porcine modeling and clinical human application demonstrated that sugammadex 2 mg/kg allows effective and rapid restoration of neuromuscular function suppressed by rocuronium. Implementation of this enhanced NMB recovery protocol assures optimal conditions for tracheal intubation as well as IONM in thyroid surgery. LEVEL OF EVIDENCE: NA.

Stimulating dissecting instruments during neuromonitoring of RLN in thyroid surgery.

OBJECTIVES/HYPOTHESIS: During intraoperative neuromonitoring (IONM) of recurrent laryngeal nerve (RLN) in thyroid surgery, the need for frequent shifting between the dissecting instruments and stimulating probe is troublesome and time-consuming. Therefore, use of these two instruments in combination would be a noticeable future direction. This study aimed to investigate the feasibility and safety of using stimulating dissecting instruments (SDIs) that combine the function of surgical dissection and nerve stimulation during IONM. STUDY DESIGN: Prospective outcomes research. METHODS: One hundred consecutive patients with 168 RLNs at risk were enrolled. We developed prototypes of SDIs and applied them to early detect adverse EMG changes during the risky phase of RLN dissection. In the case of substantial EMG change (amplitude decrease > 50%) during dissection, the surgical maneuver was paused and thyroid traction was released immediately. RESULTS: The application of SDIs was feasible in all cases and did not result in any morbidity. Nineteen RLNs were detected with substantial EMG change that was caused by traction stress during dissection with SDIs and that featured progressive gradual EMG recovery after releasing thyroid traction. After thyroid resection, 10 RLNs had a weak point of nerve conduction detected at region of Berry's ligament, but only one nerve with 79% amplitude reduction developed postoperative temporary vocal palsy. CONCLUSION: The application of SDIs is a simple and effective way to monitor the nerve's function instantly during the risky phase of RLN injury in thyroid surgery. It provides surgeons with real-time feedback of EMG response and can be applied as a tool for the early detection of adverse EMG change caused by traction distress. LEVEL OF EVIDENCE: 4.

Loss of signal in recurrent nerve neuromonitoring: causes and management.

During recurrent laryngeal nerve (RLN) neuromonitoring in thyroid surgery, laryngeal electromyography (EMG) amplitude may be correlated with the number of muscle fibers participating in the polarization and these might be correlated with the function of RLN. If RLN is severely injured during the operation, most nerve fibers do not transmit nerve impulse and substantial decrease of EMG amplitude or loss of signal (LOS) will occur. True LOS at the end of an operation often indicates a postoperative fixed vocal cord, and the surgeon should consider the optimal contralateral surgery timing in patients with planned bilateral thyroid operation to avoid the disaster of bilateral vocal cord palsy. However, LOS recovery and false LOS may occur and may lead to an unnecessary 2(nd) operation. Therefore, a reliable modality for intraoperative LOS evaluation and management would afford the surgeon real-time information that could help guide surgical procedure and planning. The updated causes, algorithm, and management of LOS during RLN neuromonitoring are reviewed and summarized.

Influence of intravenous anesthetics on neuromonitoring of the recurrent laryngeal nerve during thyroid surgery.

Limited reports are available in the literature on the impact of intravenous administration of anesthetics on laryngeal electromyographic (EMG) activity. The purpose of this study was to determine the influence of the two commonly used intravenous anesthetics (propofol and thiamylal) on EMG amplitude evoked from the recurrent laryngeal nerve (RLN) during thyroid surgery. A total of 40 patients were randomized to receive a bolus of propofol (0.5 mg/kg; n = 20) or thiamylal (1.5 mg/kg; n = 20) to increase anesthetic depth when the surgeon found patient movement intraoperatively. Evoked potentials were obtained before and every 1 minute after the administration of each agent for up to 5 minutes by stimulating the RLN. The magnitude of evoked potentials at each time point and hemodynamic response were compared within groups. The mean amplitude of evoked potentials did not change significantly after administration of either propofol or thiamylal (p > 0.05 within groups). Mean arterial pressure measured from 1 minute to 5 minutes was significantly lower in the propofol group than in the thiamylal group (p < 0.05). Heart rate measured within 5 minutes did not differ significantly within groups. Low dose of propofol (0.5 mg/kg) or thiamylal (1.5 mg/kg) did not affect EMG readings during neuromonitoring of the RLN in thyroid surgery. Our results show that thiamylal provides better hemodynamic stability than propofol, and is therefore a preferable agent to increase anesthesia depth and prevent further patient movement during intraoperative neuromonitoring.

Intraoperative neuromonitoring for the early detection and prevention of RLN traction injury in thyroid surgery: a porcine model.

BACKGROUND: Operative traction of the thyroid lobe is a necessary component of thyroid surgery. This surgical maneuver can cause traction injury of the recurrent laryngeal nerve (RLN), and this complication has been reported to be the most common mechanism of nerve injury. The goal of this study was to investigate the electromyographic (EMG) signal pattern during an acute RLN traction injury and establish reliable strategies to prevent the injury using intraoperative neuromonitoring (IONM). METHODS: Fifteen piglets (30 RLNs) underwent IONM via automated periodic vagal nerve stimulation and had their EMG tracings recorded and correlated with various models of nerve injury. RESULTS: In the pilot study, a progressive, partial EMG loss was observed under RLN tractions with different tension (n = 8). The changes in amplitudes were more marked and consistent than were the changes in latency. The EMG gradually gained partial recovery after the traction was relieved. Among the nerves injured with electrothermal (n = 4), clamping (n = 1), and transection (n = 1) models, the EMG showed immediate partial or complete loss, and no gradual EMG recovery was observed. Another 16 RLNs were used to investigate the potential of EMG recovery after different extents of RLN traction. We noted the EMG showed nearly full recovery if the traction stress was relieved before the loss of signal (LOS), but the recovery was worse if prolonged or repeated traction was applied. The mean restored amplitudes after the traction was relieved before, during, and after the LOS were 98 ± 3% (n = 6), 36 ± 4% (n = 4), and 15 ± 2% (n = 6), respectively. CONCLUSION: RLN traction injury showed graded, partial EMG changes; early release of the traction before the EMG has degraded to LOS offers a good chance of EMG recovery. IONM can be used as a tool for the early detection of adverse EMG changes that may alert surgeons to correct certain maneuvers immediately to prevent irreversible nerve injury during the thyroid operation.

Vagal nerve stimulation without dissecting the carotid sheath during intraoperative neuromonitoring of the recurrent laryngeal nerve in thyroid surgery.

BACKGROUND: Vagal nerve stimulation (VNS) has been recommended as a routine procedure during intraoperative neuromonitoring (IONM) of the recurrent laryngeal nerve (RLN). However, many surgeons have been discouraged from performing VNS because of the need for opening the carotid sheath. The purpose of this study was to investigate the feasibility and reliability of VNS without carotid sheath dissection. METHODS: Two hundred twenty patients with 376 nerves at risk were enrolled in this study. VNS without nerve exposure during IONM was applied by simply pressing a ball-tip stimulator on the space between the carotid artery and jugular vein. RESULTS: VNS without nerve exposure was feasible in all cases and did not result in any morbidity. All VNS signals were successfully obtained within 30 minutes of the start of the operation and all showed a clear and reliable laryngeal electromyography (EMG) response that was similar to that from the conventional method in which nerve exposure for VNS is applied. CONCLUSIONS: VNS without dissecting the carotid sheath is feasible and reliable, rendering it a simple, safe, and surgeon-friendly procedure during IONM.

Surgical treatment for thyrotoxic hypokalemic periodic paralysis: case report.

Thyrotoxic hypokalemic periodic paralysis (THPP) is a rare, potentially life-threatening endocrine emergency. It is characterized by recurrent muscle weakness and hypokalemia. Because many THPP patients do not have obvious symptoms and signs of hyperthyroidism, misdiagnosis may occur. The published studies revealed that definitive therapy for THPP is control of hyperthyroidism by medical therapy, radioactive iodine or surgery, but the long-term post-operative follow-up result was not observed. We reported two cases of medically refractory THPP with recurrent paralysis of extremities and hypokalemia, and both were combined with thyroid nodules. Both patients were treated with total thyroidectomy; the pathology revealed that one is Graves' disease with thyroid papillary carcinoma, and the other is adenomatous goiter with papillary hyperplasia. No episode of periodic paralysis was noted and laboratory evaluation revealed normal potassium level during the post-operative follow up. Our experience suggests that total thyroidectomy by experienced surgeon is an appropriate and definite treatment for medically refractory THPP, especially in cases combined with thyroid nodules.

Anatomical variations of recurrent laryngeal nerve during thyroid surgery: how to identify and handle the variations with intraoperative neuromonitoring.

Recurrent laryngeal nerve (RLN) palsy is the most common and serious complication after thyroid surgery. Visual identification of the RLN during thyroid surgery has been shown to be associated with lower rates of palsy, and although it has been recommended as the gold standard for RLN treatment, it does not guarantee success against postoperative vocal cord paralysis. Anatomical variations of the RLN, such as extra-laryngeal branches, distorted RLN, intertwining between branches of the RLN and inferior thyroid artery, and non-recurrent laryngeal nerve, can be a potential cause of nerve injury due to visual misidentification. Therefore, intraoperative verification of functional and anatomical RLN integrity is a prerequisite for a safe thyroid operation. In this article, we review the literature and demonstrate how to identify and handle the anatomical variations of the RLN with the application of intraoperative neuromonitoring in the form of high resolution photography, which can be informative for thyroid surgeons. Anatomical variations of the RLN cannot be predicted preoperatively and might be associated with higher rates of RLN injury. The RLN injury caused by visual misidentification can be rare if the nerve is definitely identified early with intraoperative neuromonitoring.

Intraoperative neuromonitoring for early localization and identification of recurrent laryngeal nerve during thyroid surgery.

Early and definite identification of the recurrent laryngeal nerve (RLN) is an important step to avoid inadvertent nerve injury during complicated thyroid operations. This study aimed to determine the feasibility of routine use of intraoperative neuromonitoring (IONM) to localize and identify the RLN at an early stage of thyroid surgery. This prospective study enrolled 220 consecutive patients (333 RLNs at risk) who underwent thyroid operations with application of IONM. The RLN was localized and identified routinely with a nerve stimulator after opening the space between the thyroid and carotid sheath. The success rates of early RLN localization and identification were evaluated. The current for localization and the amplitude of evoked laryngeal electromyographic signals were also recorded and analyzed. All RLNs, including 87 (26%) nerves that were regarded as difficult to identify, were successfully localized and identified. The stimulation level for RLN localization was 2mA in 315 nerves (95%) and 3mA in the other 18 nerves (5%). The signal obtained from RLN localization (amplitude = 932 ±436µV) showed a clear and reliable laryngeal electromyographic response that was similar to that from direct vagus (amplitude=811±389µV) or RLN stimulation (amplitude=1132±472µV). The palsy rate was 0.6% and no permanent palsy occurred. RLN injury is rare if the nerve is definitely identified early in the thyroid operation. The conclusion of this study is that IONM is a reliable tool for early RLN localization and identification, even in complicated thyroid operations.

Standardization of intraoperative neuromonitoring of recurrent laryngeal nerve in thyroid operation.

BACKGROUND: The lack of standardized procedures of intraoperative neuromonitoring (IONM) during thyroid operations may lead to highly variable results, and many of these results can cause misleading information and, conversely, increase the risk of recurrent laryngeal nerve (RLN) injury. Therefore, standardization of IONM procedures is necessary. METHODS: A total of 289 patients (435 nerves at risk) who underwent thyroidectomy by the same surgeon were enrolled in this study. Each patient was intubated with EMG endotracheal tube by the same anesthesiologist. Standardized IONM procedures were applied in each patient. The procedures include preoperative and postoperative video-recording of vocal cord movement, ensuring the correct position of electrodes after the neck was placed at full extension, vagal stimulation and registration of EMG signals before and after RLN dissection, and photographic documentation of the exposed RLN. RESULTS: Five patients encountered dysfunction of IONM, which was caused by malposition of electrodes and the problem was detected at once. One patient with non-RLN was detected at the earlier stage of operation. Eighteen nerves experienced loss of EMG signals during thyroid dissection, and the causes of nerve injuries were well elucidated with the application of our standardized IONM procedures. CONCLUSIONS: The standardized IONM procedures are useful and helpful not only to eliminate false IONM results, but also to elucidate the mechanism of RLN injury. After ascertaining the surgical pitfalls and improving the surgical techniques, the palsy rate was significantly reduced in this study.

Optimal depth of NIM EMG endotracheal tube for intraoperative neuromonitoring of the recurrent laryngeal nerve during thyroidectomy.

BACKGROUND: Malpositioning of the endotracheal surface electrodes can result in dysfunction of intraoperative neuromonitoring (IONM) and increase the risk of recurrent laryngeal nerve injury. The purpose of this study was to investigate the optimal depth of the nerve integrity monitor (NIM) EMG endotracheal tube. METHODS: We enrolled 105 adult patients undergoing elective thyroidectomy. Each Medtronic Xomed NIM EMG endotracheal tube was placed with the middle of the exposed electrodes well in contact with the true vocal cords under direct laryngoscopy. Function of IONM was documented and the insertion depth was measured and analyzed. RESULTS: Ninety-nine (94.3%) patients had successful IONM with the initial endotracheal tube position. Six (5.7%) patients needed further tube depth adjustment under fiberoptic bronchoscopy. All patients were finally had successful IONM. The optimal mean depth was 20.6 +/- 0.97 cm in men and 19.6 +/- 1.0 cm in women (p < 0.01). There was the trend that taller subjects had a deeper tube depth (p < 0.05). CONCLUSION: We concluded that the mean depth of the NIM EMG tube would be a useful reference value for detecting the malposition of electrodes and adjusting the depth of tube during the operation.